I'd be hesitant to say that everything after Point X is accurate. The more recent events seem to be more accurately recorded, and the less recent ones seem less accurate.
The biggest break is obviously oral vs. written history. Genesis is entirely oral tradition as far as I know, so I would expect it to be significantly less accurate than, say, Kings, Chronicles, or Samuel, which are books of written history and seem to be at least roughly in line with other sources from around that time.
During the conquest of Canaan, there are a lot of incidents where God intervenes quite directly (Jericho, stopping the sun, and various other battles). I'm loathe to say these didn't happen, but I must admit it's a fair assumption to say they were embellished somewhat.
The exiles and late OT seems to be in about the same category as the kingdom period history books - written, and reasonably on point, although unfortunately a fair number of details seem to have been changed.
The New Testament is a little different. We have literally thousands of original copies, but these weren't written down until a few decades after the event. There are minor inconsistencies here and there (the most egregious being in the nativity stories) which IMO are best explained by fallible human memory.
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In short, I believe the Bible is a spiritual document, and any historicity is mostly unnecessary. Whether or not that's the correct position I've no idea, but I think it's the safest.